Hard drugs
All hard drugs, except alcohol and cigarettes are illegal. Alcohol may only be sold to persons at least 16 years old. If you are a heroin abuser, you can get free needles and Methadone. Of course you have to prove this. Laying in the gutter appears to be insufficient for this.

Soft drugs
Soft drugs like cannabis are illegal. But you are allowed to possess or grow a small amount for "personal use". So called coffee shops in Amsterdam are allowed to sell these portions. Of course, the dealers who deliver the stuff to the shops are acting against the law.